Polyvinyl chloride (PVC) is used widely in consumer and industrial products. In the communications products industry, for example, PVC is used for conductor insulation and cable jackets. Becuase PVC is unstable when exposed to heat and light, stabilizing additives must be added to the PVC. Typically, lead-based stabilizers are employed as antidegradants in PVC compositions for wire and cable use. Generally, organic phthalate, stearate and inorganic sulfate, phosphite, or carbonate lead derivatives comprise about 2 to 5 weight percent of PVC compositions.
In practice, it has been found that these lead stabilizers confer both long term and process stability to the PVC materials. Additionally, the resulting PVC insulating and jacketing materials exhibit desirable electrical and mechanical properties.
Recently, however, there has been interest in replacing lead stabilizers in PVC lead compositions with alternative stabilizers. This interest is driven by concerns about the toxicity of the lead derivatives, the cost for disposal of hazardous plastic waste containing them, and the possibility of future legislation banning the use of lead and other heavy metals. See, for example "Heat Stabilizers: With Cadmium and Lead Drawing Fire, Suppliers Seek Alternatives", Modern Plastics, September 1990, pp. 92-99.
Although alternative stabilizer systems for PVC are known in the art, there are no reports of widely accepted alternatives to lead-based stabilizers for flexible wire and cable products, specifically, or for other applications in which the electrical properties of the PVC materials are of paramount importance. In these applications, lead-based stabilizers are the outstanding performers in conferring stability to the molecular structure of the PVC during processing. Major chemical alterations of the PVC structure, which adversely affect its electrical properties, are thereby prevented. Further, lead-based stabilizers and their reaction products with hydrogen chloride are nonconductive and are resistant to hydrolysis because of their low solubility in water. If they were otherwise, the electrical properties of the insulated conductor would be affected adversely.
In a recently developed non-lead stabilized PVC composition, lead stabilizing additives in PVC compositions for wire and cable were replaced with a synergistic mixture of oleic acid based ester lubricants in combination with a calcium-zinc composition, a tin composition or an admixture of the two metal compositions. Improvements to the foregoing were still sought after in order to improve further the electrical properties of the insulation and to reduce further the costs.
What is sought after and what seemingly is not available in the art are compositions of matter which may be used to cover transmission media such as insulation or jacketing, for example, and which include lead-free stabilizer systems that are reasonable in cost. Sought after as replacements for lead stabilizers are additives which are capable of being employed in PVC materials, and of exhibiting lower toxicity and adequate stability, and which are such that desirable electrical properties are achieved. Also, the reaction products of the sought after non-lead stabilization system should be substantially non-conductive before and after exposure to water.